happening, adj. — Green’s Dictionary of Slang

happening adj.

[rarely used 1980s + other than ironically/historically]

1. fashionable, chic, up-to-the-minute.

1967		W. Murray Sweet Ride 89: The Place was where it was happening that night.
1969		(con. 1964) N. Cohn Awopbop. (1970) 92: Murray the K: ‘You’re happening, too, baby.’ Ringo Starr: ‘O.K., we’re both happening, baby.’.
1972		D. Jenkins Semi-Tough 207: There was nobody ‘alive,’ she said. ‘Nothing is happening.’.
1989		P. Munro Sl. U. 101: happening 1. with it. hip, cool. 2. lively, fun (of a party).
1994		G. Indiana Rent Boy 110: Her chippies from like the Port of Authority in the clothes they change into to become hip and happening.
2005		‘Doonesbury’ in Guardian G2 10 Nov. 29: Back in the day he was happenin’! Bell bottoms, Donovan records, crunchy politics.
2018		I. Welsh Dead Man’s Trousers [suimmer 2016]: He’s never gaunny play for Hibs, though, or front a happening band.

2. of an event, a creation, working out as desired.

2003		W. Zanes Dusty in Memphis 10: But what I grasped and what I didn’t grasp at that point didn’t matter. The album was happening.
2005		B. Coleman Rakim Told Me 123: ‘We would sometimes stop in mid-air on a track and then trash the whole thing and start again. [...] We'd all take a vote to see if we thought it was happening, and if it wasn’t then we'd move on’.
2018		W. Kramer Hard Stuff 92: That night, the excitement in the Grande was through the roof. It was all happening for the MC5.

what’s happening (also that’s what’s happening)

(orig. US black) the fashionable, chic, smart event, place, show etc; thus not what’s happening, the opposite.

1961		N. Hentoff Jazz Life 158: A lot of musicians think the public is stupid, but audiences know what’s happening.
1967		M.S. Brookins ‘Aspiration’ in Kochman Rappin’ and Stylin’ Out (1972) 381: Big Time was it. He was in, baby—really what was happening.
1969		N. Cohn Awopbop. (1970) 92: You’re what’s happening, baby.
1975		E. Torres Carlito’s Way 71: [A]ll the better for the guys that really knew what’s happening. That’s money, baby, money.
1980		E. Folb Runnin’ Down Some Lines 260: what’s happening 1. What it is important to know. 2. What it is important to do in order to succeed or survive. 3. What is in fashion. 4. What is appropriate to a situation (see happenings).
1992		Bentley & Corbett Prison Sl. 47: That’s What’s Happenin’ The ultimate or absolute best in goods or services. ‘I’d like to have a brand new, red Corvette convertible. Now that’s what’s happenin.’.